Cheap solutions to networking problems don't really exist unfortunately. You could try a band-aid solution like powerline, but there is no guarantee that it works better than wi-fi. It could. It's not as expensive as a renovation. https://www.amazon.de/-/en/Powerline-TL-PA7017P-KIT-Compatible-Energy-Saving/dp/B0859MDSFX/ref=sr_1_5?crid=1CT7MY83ACLG7&keywords=powerline&qid=1667312757&qu=eyJxc2MiOiI0Ljg0IiwicXNhIjoiNC40NiIsInFzcCI6IjQuMjMifQ%3D%3D&sprefix=powerlin%2Caps%2C178&sr=8-5